U.S. Patent Application Publication No. 2005/0017290 discloses a reverse-conducting semiconductor device, which is also called a reverse-conducting insulated gate bipolar transistor 10 (RC-IGBT). The RC-IGBT 10 includes, within one wafer, an insulated gate bipolar transistor (IGBT) with a built-in freewheeling diode. As shown in FIG. 1, the RC-IGBT 10 includes a base layer 1 formed as an n-type base layer with a emitter side 101 and a collector side 102 opposite the emitter side 101. A fourth p-type layer 4 is arranged on the emitter side 101. A fifth n-type layer 5 is arranged on the fourth layer. The fifth layer 5 has a higher doping than the base layer 1 is arranged on the emitter side 101.
A sixth electrically insulating layer 6 is arranged on the emitter side 101. The sixth layer 6 covers the fourth layer 4 and the base layer 1, and partially covers the fifth layer 5. An electrically conductive seventh layer 7 is completely embedded in the sixth layer 6. No portion of the fifth or sixth layer 5, 6 is arranged above the central part of the fourth layer 4.
A first electrical contact 8 is arranged on the central part of the fourth layer 4. The first electrical contact 8 covers the sixth layer 6. The first electrical contact 8 is in direct electrical contact with the fifth layer 5 and the fourth layer 4, but is electrically insulated from the seventh layer 7.
On the collector side 102, a buffer layer 13 is arranged on the base layer 1. On the buffer layer 13, n-type third layers 3 and p-type second layers 2 are arranged alternately in a plane. The third layers 3 and the buffer layer 13 have a higher doping than the base layer 1. The third layers 3 are arranged directly below the fourth layer 4 and the first electrical contact 8 if seen in an orthographic projection.
A second electrical contact 9 is arranged on the collector side 102. The second electrical contact 9 covers the second and third layers 2, 3 and is in direct electrical contact with the second and third layers 2, 3.
In such a reverse-conducting semiconductor device 10, a freewheeling diode is formed between the second electrical contact 9, part of which forms a cathode electrode in the diode, the third layer 3, which forms a cathode region in the diode, the base layer 1, part of which forms a base layer in the diode, the fourth layer 4, part of which forms an anode region in the diode, and the first electrical contact 8, which forms an anode in the diode.
An IGBT is formed between the second electrical contact 9, part of which forms a collector electrode in the IGBT, the second layer 2, which forms a collector region in the IGBT, the base layer 1, part of which forms a base layer, the fourth layer 4, part of which forms a p-base region in the IGBT, the fifth layer 5, which forms a source region in the IGBT, and the first electrical contact 8, which forms an emitter electrode. During an on-state of the IGBT, a channel is formed between the emitter electrode, the source region and the p-base region towards the n-base layer.
The layers of the RC-IGBT on the collector side 102 can be manufactured by implanting and diffusing p-type ions. Afterwards, a resist mask, which is attached to the wafer, is introduced, through which n-type ions are implanted and afterwards diffused. The implantation dose of the n-type ions has to be so high that it compensates the p-type region. The p- and n-type implantation steps can also be reversed.
DE 198 11 568 discloses an IGBT and a manufacturing method for such an IGBT with a built-in MOSFET, which includes on the backside an alternating p-doped third layer and an n-doped second layer. These layers are arranged in different, not overlapping planes. A p-doped third layer is formed, and recesses are formed in the third layer by etching. N-type ions are then implanted over the whole backside surface, and afterwards a heat treatment is performed, by which the n- and p-type layers are created. Therefore, the n-type ions are also implanted on those parts, on which p-type ions are arranged, which implies that the p-dose has to be higher than the n-dose.
In another manufacturing method described in DE 198 11 568, recesses are first created, then the second main side is irradiated in those parts without recess with electrons or protons, and afterwards phosphorous ion implantation is performed over the whole surface. Then p doped ions are implanted into that part without recesses, so that again the dose of the p-type ions has to be higher than the n dose. A heat treatment is performed for forming the n-type second layer and p-type third layer.
Due to the necessary overcompensation, limited selection for dose and depth of the latter manufactured layer of the second and third layers 2, 3 are only possible, and the control for the injection efficiencies of the p- and n-type regions is unsatisfactory. On-state snap-back effects, which are defined by the point at which the conduction voltage and current characteristics change from MOS operation mode to IGBT operation mode, can occur, which are undesirable for the device in the IGBT mode. FIG. 7 shows the output characteristics of the RC-IGBT current Ic to voltage Vce. The dashed line 14 shows the strong overshoot resulting from the snap-back effect, as it is typical for a conventional RC-IGBT during the change from MOS to IGBT operation mode. FIG. 8 shows the RC-IGBT current waveform in the diode mode during reverse recovery of the device. A conventional RC-IGBT shows a snappy behavior of the device during reverse recovery (dotted line 17). The snappy behavior is also present during turn-off for the IGBT as well as for the diode reverse recovery.